Mapping the nonlinear stress propagation in topological polymer blends
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Excerpt of abstract: Entangled polymers and blends of varying topologies and stiffnesses exhibit complex nonlinear rheological properties that depend on the blend composition and the scale of the strain. How local nonlinear stresses propagate through these systems remains an open question. Here, we combine optical tweezers microrheology with fluorescence imaging and differential dynamic microscopy (DDM) to map the deformation field arising from a local nonlinear strain in entangled polymer blends. We use optical tweezers to impart local nonlinear strains and measure the resulting stresses during and following strain. We simultaneously image labeled DNA molecules surrounding the strain site and use DDM to determine how the macromolecular dynamics vary with distance from the applied strain. We perform these measurements on entangled solutions of linear and ring DNA, as well as blends of DNA and microtubules. Our approach, which combines active microrheology with macromolecular tracking and differential dynamic microscopy, directly links nonlinear stress propagation to macromolecular deformations and dynamics, and is applicable to a wide range of complex fluids and polymeric materials.